Title

Authors

Publication Date

1-1-1987

Series Number

58

Abstract

Geophysical surveys and drilling were used to investigate a saline valley on Allandale Research Farm. These techniques showed that the geology is controlling the location of two main areas of saline seeps and they identified another area at risk of increased salinity. They were also used to obtain information on the groundwater system and to assist in making management recommendations.

Electromagnetic terrain conductivity surveys showed that the most saline soils occurred upstream of a cross-cutting magnetic anomaly caused by a dolerite dyke. A seismic survey showed that the anomaly coincided with a bedrock rise. This bedrock rise restricts groundwater flow through the catchment and forces saline groundwater to the surface where it evaporates causing salts to build up in the soil profile. A second area of saline surface soils occurs further downstream. Outcrops of granite in the creek indicate that another bedrock rise is the cause for the location of this seep. A third area in the valley upslope from the main saline area has a high subsoil conductivity and is immediately upslope of a second magnetic anomaly. This area may become more saline in the future.

Drilling confirmed the seismic profile near the dolerite dyke in the main saline area. It also indicated that deep groundwater pressures are above ground level along the whole of the valley/ becoming higher with increased distance downstream. The quality of the groundwater ranged from 3,500 to 6,500 mg.Cl-1/L.

Three recommendations are made for the area:

(i) the construction of an interceptor drain/ upslope of each saline area, to reduce waterlogging;